1. Field of the Invention
This invention generally relates to digital communications and, more particularly, to the aggregation of 10GBASE-R channels into single pseudo 100GBASE-R channels that may be transported over links designed for 100GBASE-R channels.
2. Description of the Related Art
802.3ba: IEEE Std 802.3ba™-2010.
802.3: IEEE Std 802.3™-2008.
10G: 10 gigabits per second (Gbps). As used herein, all rates and bandwidths are defined as being nominal or as approximately accurate.
100G: 100 gigabits per second (Gbps).
10GBASE-R: This is a signaling protocol defined by IEEE 802.3 in IEEE-802.3-2008 for serial transmission of a 100 data stream across various media.
100GBASE-R: This is a signaling protocol defined by 802.3ba for transmission of an aggregate 100G data stream across various media using one (100G), two (50G), four (25G), five (200), or ten (100) physical lanes.
10GBASE-R channel: An independent 10G data stream with 10GBASE-R formatting.
100GBASE-R channel: An independent 100G data stream with 100GBASE-R formatting.
100GBASE-R logical lane: 100GBASE-R PCS lane as specified in the 802.3ba. 100GBASE-R is composed of 20 5 Gbps logical lanes that may be multiplexed together for transport over higher rate lanes.
100GBASE-R physical lane: 100GBASE-R is transported over links composed of 1, 2, 4, 5, 10, or 20 physical lanes. Each 100GBASE-R physical lane is composed of 1 or more 100G logical lanes. For instance, in a CAUI-10 interface there are 10 physical lanes of 10 Gbps each composed of 2 100GBASE-R logical lanes each.
10GBASE-R link: A physical connection between two devices or end points, e.g., 10GBASE-SR.
100GBASE-R link: A physical connection between two devices or end points, e.g., CAUI-10 or 100GBASE-SR4.
CAUI-10: An inter-device connection for 100G Ethernet as specified in 802.3ba Annex 83A and 83B, where it is referred to as CAUI. The label CAUI-10 is used in this document instead of CAUI, to explicitly differentiate it from CAUI-4 described below.
CAUI-4: This is a physical instantiation of 100 in 4 lanes across a copper medium for interconnection between a MAC device and a PHY device, or between a pair of PHY devices typically on the same board or between a device on a board and a physical module. The physical requirements of CAUI-4 are not defined by IEEE 802.3 at the time of this writing, but as used herein, it is a 4-lane instantiation of 100GBASE-R % (as defined above). As used herein, CAUI-4 is intended to also include other similar interfaces such as CPPI-4 (yet to be defined by IEEE 802.3) and OIF-28G-VSR.
AM: Alignment marker as defined for 100GBASE-R in 802.3 Clause 82. The AM is a special 64B/66B block.
PCS: Physical coding sub-layer as defined in 802.3.
PMA: Physical medium attachment sub-layer defined in 802.3.
PMD: Physical medium dependent sub-layer defined in 802.3.
CFP: The first generation of standardized module type for 100G Ethernet transceivers using a 10×10G host interface.
CFP2: The yet to be defined, second generation of standardized module type for 100G Ethernet transceivers using a 4×25G host interface.
Inter-frame: In Ethernet data streams, this is as defined in 802.3 is the signal content between Ethernet packets defined as being between the last byte of the MAC packet FCS and the last byte before the preamble of the next MAC packet and includes the /T/ character. In 10GBASE-R this content may be IDLE ordered sets, sequence ordered sets, signal order sets or control ordered sets (e.g., error codes). For the purposes of rate adaptation groups of 4 IDLE characters (IDLE order sets) may be inserted or IDLE ordered sets and sequence ordered sets may be deleted.
Sequence ordered set: This is a 4-octet group of bytes a described in 802.3 Clause 46.
Block: A 64B/66B block as defined for 10GBASE-R in 802.3 Clause 49 and for 100GBASE-R in 802.3ba Clause 82. This is a 66-bit block with a two-bit sync header and 64-bit payload.
FIFO: First-in-first-out buffer is a buffer with an input and output. The buffer is flexible in size. As words are input the buffer fills. Words are read out in the same order that they are put into the buffer.
CPPI: 100G parallel physical interface between PMA and PMD on a PCB. CPPI is specified in IEEE 802.3ba-2010 Annex 86A as a 10-lane interface. As used herein, other non-standard lane widths (CPPI-N) such as CPPI-4 with 4 25G per lane are also considered.
Attachment interface: A general term encompassing various inter-device interfaces such as CAUI-4, CAUI-10, and CPPI-N, defined above.
FIG. 1 is a schematic block diagram depicting a 10×10G interconnection between a medium access control (MAC) device and a line interface module (prior art). Conventional implementations of 100G modules designed for transport of 100G Ethernet connect a 100G MAC device through a CAUI-10 interface with 10 physical lanes of 10 Gbps each. The CAUI-10 interface may be configured as either a single 100GBASE-R link striped across 10 physical lanes (per 802.3ba) carrying signal 100GBASE-R channel, or it can be configured as 10 independent 10GBASE-R links carrying a single 10GBASE-R channel on each link.
If the line side of the module is a 100GBASE-R link, then the 100GBASE-R channel on the system side is mapped to and from the 100GBASE-R link on the line side. If the line side of the module is 10 GBASE-R links, then each of the 10GBASE-R channels on the system side may be mapped directly to one of the 10GBASE-R links on the line side.
FIG. 2 is a schematic block diagram of a 4×25G interconnect between a MAC device and a line interface module (prior art). Note: a 4×25G interface is likely to be standardized after the filing of this application. Proposed generations of line interface modules may condense the attachment interface to 4 physical lanes of 25 Gbps each. There will, therefore, no longer be a one-to-one mapping from a 10GBASE-R link on the system side to a 10GBASE-R link on the line side. Instead, 2.5 10GBASE-R channels must be mapped into each 25G physical lane. At the time of this writing there is no common or publically known method for aggregating 2.5 10GBASE-R channels into each 25G physical lane, while retaining the signaling rate and format of the 100GBASE-R channel. This issue was identified as unresolved in the Jun. 12, 2011 meeting of the Optical Internetworking Forum PLL working group.
It would be advantageous if 10 10GBASE-R channels could be transparently transported over links designed for 100GBASE-R without modifying the data content of the 10GBASE-R channels. For example, it would be advantageous if 10 10GBASE-R channels could be transported over multi-lane 100G attachment interfaces such as a 4-lane by 25 Gbps CAUI-4 interface. As another example, it would be advantageous if 10 10GBASE-R channels could be carried over a 100GBASE-R electrical or optical link operating at 100 Gbps.